1. Technical Field
The invention relates to the use of fiber optics for the illumination of analyte samples and for the detection of signals present at such analyte samples. More particularly, the invention relates to fiber optic illumination and detection patterns, shapes, and locations for use in the noninvasive global-estimation of analytes, such as blood glucose.
2. Description of the Prior Art
To those knowledgeable in the art, the size, arrangement, and number of detection and illumination optical fibers at the interface of a probe designed to launch and collect light from a tissue sample, such as human skin, significantly impacts the received signal.
Various attempts have been made in the past to provide devices that illuminate and collect light from a tissue sample. See, for example, K. Maruo, K. Shimizu, M. Oka, Device For Non-Invasive Determination of Glucose Concentration in Blood, European Patent Application No. EP 0 843 986.
However, such known devices have provided less than satisfactory results. It would be advantageous to provide a method and apparatus for optimizing fiber optic illumination and detection patterns, shapes, and locations for use in the noninvasive prediction of analytes, such as blood glucose.
The invention provides a method and apparatus for optimizing fiber optic illumination and detection patterns, shapes, and locations for use in the noninvasive prediction of analytes, such as blood glucose. If the optical system is appropriately modeled, the received signal can be predicted. By systematically exploring patterns, shapes, and fiber locations, the invention herein disclosed makes it possible to optimize the optical system design by maximizing desirable quantities in a system model, for example the signal-to-noise ratio (SNR).
In the example of the signal-to-noise ratio, the signal is directly related to the photon pathlength in the subject""s dermis and the noise is approximately inversely proportional to the intensity as a function of wavelength and detector to illumination fiber separation distance. Additionally, the number of fibers at a monochromator output slit and at the bundle termination at a detector optics stack can be determined, causing the optimization to become particularly constrained. Once this constraint is in place, it becomes significantly easier for the pattern of illumination and detection fibers to be investigated and optimized. Finally, the shape of the perimeter of the fiber layout is dictated by simple geometrical considerations.
Throughout this process, fabrication constraints should be ignored whenever possible. Only after arriving at an optimal solution can tradeoffs concerning tolerable losses for the sake of practicality and expediency be properly addressed.